It is broadly old to dynamically relocate code at runtime given that the code to be executed is larger than the available internal memory of a computing facility. Segmentation, overlays, and libraries are among the mechanisms which permit nonresident code to be called in from external memory, such as DASD, only as needed. However, the binding of the code to internal memory addresses must still be imposed on all of such referenced segmentations, overlays, and library elements.
Peterson and Silberschatz, "Operating System Concepts", Addison-Wesley Publishing Co., copyright 1983, pp. 137-139, describe one method of dynamically managing code relocation in which internal memory address binding of the code is delayed until execution (runtime). The code is mapped in Peterson's scheme into a linear address space formed by a base plus an offset to that base. In this regard, the base is supplied by a dedicated register, while the offset is supplied extrinsically.
Another method of dynamically managing code relocation in which address binding is delayed until runtime is set out in Drogichen, U.S. Pat. No. 4,138,738, "Self-contained Relocatable Memory Subsystem", issued Feb. 6, 1979. Drogichen teaches that ROM-stored code/data sequences may be relocated in CPU internal store if additional stored bits appending each code/data word are used to designate a set of external registers. The contents of these designated registers are operands in the computation of an effective internal memory address for the counterpart code/data word being moved.
In the field of data base management systems, C. J. Date, "A Guide to DB2", Addison-Wesley Publishing Co., copyright 1984, discloses the compile and runtime involvements of the elements of a relational system for accessing information. The information typically is located on a staged storage system and is obtained by way of a computing facility. The data is organized by the computing facility under any one of the popular storage and accessing methods such as IMS, VSAM, or ISAM. Relational accessing is executable in either an interactive or deferred execution mode. As Date points out, relational accessing has provided a popular and flexible manner by which subsets of data are obtained by imposing relations through a query. The advantage of relational accessing is that a near-infinite number of relations can be imposed upon data without the necessity of storing concordances representing those relations.
When a data base system is operated in an interactive mode, an access statement is processed by the data base manager interpretively by way of tables. Since the tables per se are not stored on a persistent medium, such as DASD, they must be formed each time and made resident in main memory for the duration of the interactive processing. There is no perceived need for relocation. In contrast, deferred accessing involves relational statements which are embedded in an application. The application itself may be executable at multiple disparate times. For this reason, optimized compiled machineexecutable code is a necessary condition for such processing. When the application is being compiled, the control blocks, such as skeleton cursor tables, constituting each relational access are formed and associated with or "bound" to the application. These skeleton control blocks are then stored on a persistent medium, such as DASD. At execution or "runtime", the control blocks must then be relocated from DASD to main memory in a form ready for utilization.
A relational system includes more than merely a compiler and link loader. It is, according to Date, formed from a precompiler, a binder, a runtime supervisor, and a stored data manager. The precompiler collects relational accessing statements from application programs and forms data base request modules. The accessing statements in the original program are replaced by host language calls to the runtime supervisor. The binder is the active component responsive to each of the request modules for producing optimized machine-executable code implementing the relational accessing statements. This code is generated in the form of control blocks which may be considered as a specialized form of a linked list.